In Traditional Chinese Medicine (TCM), Xiang Fu belongs to the 'Herbs that regulate Qi' category. Herbs in this category typically treat a TCM condition called 'Qi Stagnation'. Concretely it means that Qi is blocked in the body's Organs and Meridians, most typically the Stomach, Liver, and to a lesser extent, the Lungs. In modern medicine terms, Qi Stagnation often translates into psychological consequences such as depression, irritability or mood swings. It's also frequently associated with conditions such as premenstrual syndrome (PMS), menopausal symptoms, the development of breast swellings as well as various digestive disorders.
Furthermore Xiang Fu is Neutral in nature. This means that Xiang Fu typically doesn't affect the balance in your body. Balance between Yin and Yang is a key health concept in TCM. Eating too many "Hot" (Yang) ingredients can lead to an imbalance whereby one has a Yang Excess. The inverse is true as well: too many "Cold" (Yin) ingredients can lead to a Yin Excess. The Neutral nature of Xiang Fu means that you don't have to worry about that!
Xiang Fu also tastes Bitter, Pungent and Sweet. The so-called 'Five Phases' theory in Chinese Medicine states that the taste of TCM ingredients is a key determinant of their action in the body. Bitter ingredients like Xiang Fu tends to have a cleansing action on the body by clearing Heat, drying Dampness and promoting elimination via urination or bowel movements. On the other hand Pungent ingredients tend to promote the circulations of Qi and Body Fluids. That's why for instance someone tends to sweat a lot when they eat spicy/pungent food. Lastly Sweet ingredients tend to slow down acute reactions and detoxify the body. They also have a tonic effect because they replenish Qi and Blood.
The tastes of ingredients in TCM also determine what Organs and Meridians they target. As such Xiang Fu is thought to target the Liver, the Sanjiao and the Spleen. In TCM the Liver is often referred as the body's "general" because it is in charge of regulating the movements of Qi and the Body Fluids. It also takes a leading role in balancing our emotions. The Triple Burner (Sanjiao) is a special concept in TCM with no corresponding organ in modern medicine. Its function is similar to a water wheel: Body Fluids, Qi and food are transported through the San Jiao and that very movement helps our metabolism. The Spleen assists with digestion, Blood coagulation and Fluids metabolism in the body.